Individually compliant segments for split ring hydrodynamic face seal

ABSTRACT

Embodiments of the present disclosure are directed toward a face seal including a stator ring configured to be disposed about a rotor of a turbine, wherein the stator ring includes a first ring segment and a second ring segment which are circumferentially split and configured to cooperatively form the stator ring, and bearing elements disposed between the first and second ring segments and configured to enable relative axial motion between the first and second ring segments at interfaces between the first and second ring segments. The stator ring further includes hydrodynamic surface features on surfaces of the first and second ring segments configured for facing the rotor, wherein the hydrodynamic surface features comprise Y-shaped grooves each comprising a stem portion extending from a middle region of stator ring and splitting into inner and outer branches extending towards inner and outer diameters of the stator ring and terminating prior to the inner and outer diameters.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims priority to U.S.Non-Provisional application Ser. No. 14/226583, entitled “INDIVIDUALLYCOMPLIANT SEGMENTS FOR SPLIT RING HYDRODYNAMIC FACE SEAL,” filed on 26Mar. 2014, and published as US20150275684, the disclosure of which ishereby incorporated by reference.

BACKGROUND

The subject matter disclosed herein relates to turbomachines, and, moreparticularly, to face seals for reducing or blocking flow leakagebetween various components of a turbomachine.

Turbomachines include compressors and/or turbines, such as gas turbines,steam turbines, and hydro turbines. Generally, turbomachines include arotor, which may be a shaft or drum, which support turbomachine blades.For example, the turbomachine blades may be arranged in stages along therotor of the turbomachine. The turbomachine may further include variousseals to reduce or block flow (e.g., working fluid flow) leakage betweenvarious components of the turbomachine. For example, the turbomachinemay include one or more face seals configured to reduce or block flowleakage between the shaft (e.g., rotating shaft) and a housing of theturbomachine. Unfortunately, traditional face seals may be difficult toassemble and/or may be susceptible to large face deformation that mayresult in premature wear or performance degradation.

BRIEF DESCRIPTION

In one embodiment, a system includes a steam turbine and a face seal ofthe steam turbine. The face seal comprises a rotor ring coupled to arotor of the steam turbine; and a stator ring coupled to a stationaryhousing of the steam turbine, wherein the stator ring iscircumferentially split into a plurality of circumferential segmentswith one or more bearing elements disposed between each of the pluralityof circumferential segments, wherein the one or more bearing elementsare configured to enable relative axial movement of the plurality ofsegments relative to one another. The face seal further compriseshydrodynamic surface features on a sealing surface of at least one ofthe rotor ring and the stator ring facing the other of the rotor ringand the stator ring. The hydrodynamic surface features comprise Y-shapedgrooves each comprising a stem portion extending from a middle region ofthe rotor ring or the stator ring and splitting into inner and outerbranches extending towards inner and outer diameters of the rotor ringor the stator ring respectively

In another embodiment, a turbine comprises a rotor, a stationary housingdisposed about the rotor, and a face seal disposed about the rotor. Theface seal comprises a rotor ring coupled to or integral with the rotor;and a stator ring coupled to the stationary housing. The stator ringcomprises a first segment, a second segment, and at least two bearingelements, wherein the first and second segments are circumferentiallysplit, and the at least two bearing elements are disposed between thefirst and second segments, and wherein the first segment, the secondsegment, and the at least two bearing elements cooperatively form thestator ring. The stator ring further comprises hydrodynamic surfacefeatures on a sealing surface of at least one of the rotor ring and thestator ring facing the other of the rotor ring and the stator ring. Thehydrodynamic surface features comprise Y-shaped grooves each comprisinga stem portion extending from a middle region of the rotor ring or thestator ring and splitting into inner and outer branches extendingtowards inner and outer diameters of the rotor ring or the stator ringrespectively.

In another embodiment, a system includes a stator ring configured to bedisposed about a rotor of a turbine, wherein stator ring comprises afirst ring segment and a second ring segment which are circumferentiallysplit and configured to cooperatively form the stator ring, and at leastone bearing element disposed between the first and second ring segmentsand configured to enable relative axial motion between the first andsecond ring segments at interfaces between the first and second ringsegments. The stator ring further comprises hydrodynamic surfacefeatures on surfaces of the first and second ring segments configuredfor facing the rotor, wherein the hydrodynamic surface features compriseY-shaped grooves each comprising a stem portion extending from a middleregion of stator ring and splitting into inner and outer branchesextending towards inner and outer diameters of the stator ring andterminating prior to the inner and outer diameters.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic of an embodiment of a combined cycle powergeneration system having a gas turbine system, a steam turbine, and aheat recovery steam generation (HRSG) system;

FIG. 2 is a partial cross-sectional view of an embodiment of a steamturbine, illustrating a face seal of the steam turbine;

FIG. 3 is a partial cross-sectional view of a turbomachine, illustratingan embodiment of a face seal of the turbomachine;

FIG. 4 is a perspective view of an embodiment of a primary sealing ringof the face seal, illustrating a split-ring configuration of the primarysealing ring;

FIG. 5 is a partial cross-sectional view of a turbomachine, illustratingan embodiment of a face seal of the turbomachine;

FIG. 6 is a perspective view of an embodiment of a primary sealing ringof the face seal, illustrating locally compliant sealing pads of theprimary sealing ring;

FIG. 7 is a perspective view of an embodiment of a primary sealing ringof the face seal, illustrating locally compliant sealing pads of theprimary sealing ring;

FIG. 8 is a perspective view of an embodiment of a primary sealing ringof the face seal, illustrating locally compliant sealing pads of theprimary sealing ring;

FIG. 9 is a partial perspective view of an embodiment of a primarysealing ring of the face seal, illustrating a spring biasing a locallycompliant sealing pad of the primary sealing ring;

FIG. 10 is a perspective view of an embodiment of a primary sealing ringof the face seal, illustrating an arrangement of locally compliantsealing pads of the primary sealing ring;

FIG. 11 is a perspective view of an embodiment of a primary sealing ringof the face seal, illustrating an arrangement of locally compliantsealing pads of the primary sealing ring;

FIG. 12 is a perspective view of an embodiment of a primary sealing ringof the face seal, illustrating a surface feature of the primary sealingring; and

FIG. 13 is a perspective view of an embodiment of a primary sealing ringof the face seal, illustrating a surface feature of the primary sealingring.

DETAILED DESCRIPTION

Embodiments of the present disclosure are directed toward improved faceseals having features configured to reduce leakage across the face sealand improve performance and longevity of the face seal. As will beappreciated, the face seal may include a primary ring (e.g., astationary ring) which forms a sealing relationship or interface with amating ring (e.g., a rotating ring). For example, the primary ring andthe mating ring may be configured to reduce or block leakage of aworking fluid across the face seal. In certain embodiments, the primaryring may have a split configuration with a bearing element, such asrolling interface. More specifically, the primary ring may include twoor more segments which cooperatively form the primary ring, and theprimary ring may include one or more rolling interfaces (e.g., bearingelements) between the two or more segments. For example, one or morepins or other rounded elements may be disposed between the two or moresegments when the two or more segments are in abutment with one another.In the manner described below, the bearing element (e.g., rollinginterface) between the two or more segments may enable low-frictionrelative movement (e.g., axial movement) between the two or moresegments of the primary ring. In this way, each of the segments of theprimary ring may achieve its own hydrodynamic equilibrium with respectto the mating (e.g., rotating) ring of the face seal. Furthermore, therolling interfaces of the primary ring may be configured to absorb orsupport a radial pressure or load from each of the segments of theprimary ring.

In certain embodiments, the primary ring of the face seal may includelocally compliant hydrodynamic pads configured to engage with the matingring. That is, each of the locally compliant hydrodynamic pads of theprimary ring may be configured to form a separate sealing relationshipwith the mating ring. Specifically, each of the hydrodynamic pads may beindividually biased toward the mating ring (e.g., by a spring coupled tothe primary ring). In this way, each of the hydrodynamic pads canindividually conform to the dynamically changing orientation of themating ring, thereby improving the overall sealing interface and leakblockage between the primary ring and the mating ring. Additionally, thehydrodynamic pads may ensure that the segmented primary ring closes intoward the mating ring in a more uniform manner to avoid cocking orpartial contacting between the primary ring and mating ring.Additionally, as described in detail below, each of the hydrodynamicpads may block direct contact between the primary ring and the matingring while also reducing elevated leakage gaps.

It should be noted that in the following discussion, reference may bemade to contact between various components of the face seal (e.g.,primary ring, mating ring, hydrodynamic pads, etc.). However, it shouldbe appreciated that reference to contact between such components mayencompass very small gaps (e.g., 0.01-0.25 mm gaps) between suchcomponents, or parts of the components, rather than actual contactbetween such components.

Turning now to the drawings, FIG. 1 is a schematic block diagram of anembodiment of a conventional combined cycle system 10 having variousturbomachines in which face seals of the present disclosure may be used.Specifically, the turbomachines may include face seals which may includea primary ring having a split configuration with rolling interfacesand/or a primary ring with locally compliant hydrodynamic pads. Asshown, the combined cycle system 10 includes a gas turbine system 11having a compressor 12, combustors 14 having fuel nozzles 16, and a gasturbine 18. The fuel nozzles 16 route a liquid fuel and/or gas fuel,such as natural gas or syngas, into the combustors 14. The combustors 14ignite and combust a fuel-air mixture, and then pass hot pressurizedcombustion gases 20 (e.g., exhaust) into the gas turbine 18. The turbineblades 22 are coupled to a rotor 24, which is also coupled to severalother components throughout the combined cycle system 10, asillustrated. For example, the turbine blades 22 may be arranged instages. In other words, the turbine blades 22 may be circumferentiallyarranged about the rotor 24 at various axial locations of the rotor 24.As the combustion gases 20 pass through the turbine blades 22 in the gasturbine 18, the gas turbine 18 is driven into rotation, which causes therotor 24 to rotate along a rotational axis 26. In certain embodiments,the gas turbine 18 may include face seals configured to reduce or blockundesired leakage of the combustion gases 20 across rotor-stator gapswithin the turbine. Eventually, the combustion gases 20 exit the gasturbine 18 via an exhaust outlet 28 (e.g., exhaust duct, exhaust stack,silencer, etc.).

In the illustrated embodiment, the compressor 12 includes compressorblades 30. The compressor blades 30 within the compressor 12 are alsocoupled to the rotor 24 and rotate as the rotor 24 is driven intorotation by the gas turbine 18 in the manner described above. As withthe turbine blades 22, the compressor blades 30 may also be arranged instages. As the compressor blades 30 rotate within the compressor 12, thecompressor blades 30 compress air from an air intake into pressurizedair 32, which is routed to the combustors 14, the fuel nozzles 16, andother portions of the combined cycle system 10. Additionally, thecompressor 12 may include face seals configured to block undesiredleakage of the pressurized air 32 across various rotor-stator gapswithin a compressor.

The fuel nozzles 16 mix the pressurized air 32 and fuel to produce asuitable fuel-air mixture, which combusts in the combustors 14 togenerate the combustion gases 20 to drive the turbine 18. Further, therotor 24 may be coupled to a first load 34, which may be powered viarotation of the rotor 24. For example, the first load 34 may be anysuitable device that may generate power via the rotational output of thecombined cycle system 10, such as a power generation plant or anexternal mechanical load. For instance, the first load 34 may include anelectrical generator, a propeller of an airplane, and so forth.

The system 10 also includes a steam turbine 36 for driving a second load38 (e.g., via rotation of a shaft 40 of the steam turbine 36). Forexample, the second load 38 may be an electrical generator forgenerating electrical power. However, both the first and second loads 34and 38 may be other types of loads capable of being driven by the gasturbine system 11 and the steam turbine 36. In addition, although thegas turbine system 11 and the steam turbine 36 drive separate loads(e.g., first and second loads 34 and 38) in the illustrated embodiment,the gas turbine system 11 and steam turbine 36 may also be utilized intandem to drive a single load via a single shaft.

The system 10 further includes the heat recovery steam generator (HRSG)system 42. Heated exhaust gas 44 from the gas turbine 18 is transportedinto the HRSG system 42 to heat water to produce steam 46 used to powerthe steam turbine 36. As will be appreciated, the HRSG system 42 mayinclude various economizers, condensers, evaporators, heaters, and soforth, to generate and heat the steam 46 used to power the steam turbine36. The steam 46 produced by the HRSG system 42 passes through turbineblades 48 of the steam turbine 36. As similarly described above, theturbine blades 48 of the steam turbine 36 may be arranged in stagesalong the shaft 40, and the steam turbine 36 may include face seals toblock undesired leakage of steam 46 across various rotor-stator gapswithin the steam turbine 36. As the steam 46 pass through the turbineblades 48 in the steam turbine 36, the turbine blades 48 of the steamturbine 36 are driven into rotation, which causes the shaft 40 torotate, thereby powering the second load 38.

In the following discussion, reference may be made to various directionsor axes, such as an axial direction 50 along the axis 26, a radialdirection 52 away from the axis 26, and a circumferential direction 54around the axis 26 of the compressor 12, the gas turbine 18, or steamturbine 36. Additionally, as mentioned above, while the face sealsdescribed below may be used with any of a variety of turbomachines(e.g., compressors 12, gas turbines 18, or steam turbines 36) thefollowing discussion describes improved face seals in the context of thesteam turbine 36.

FIG. 2 is a partial cross-sectional view of the steam turbine 36,illustrating a position of a face seal 100 within the steam turbine 36.As mentioned above, the steam turbine 36 may include one or more faceseals 100 for reducing or blocking leakage of a working fluid (e.g.,steam 46) across various rotor-stator gaps within the steam turbine 36.

In the illustrated embodiment, the steam turbine 36 includes a casing60, an inner shell 62, and sealing components 64 disposed about theshaft 40 of the steam turbine 36. As shown, steam 46 enters the steamturbine 36 through an inlet 66 to an inlet side 68 of the steam turbine36. As described above, the steam 46 may drive rotation of the turbineblades 48, thereby driving rotation of the shaft 40. As shown, some ofthe sealing components 64 form a tortuous path (e.g., a tortuous sealingpath) between a stator component 70 of the steam turbine 36 and theshaft 40 of the steam turbine 36. As will be appreciated, although thesteam 46 is directed towards the turbine blades 48 within the steamturbine 36, a portion of the steam 46 may leak through a leakage region72 of the steam turbine 36, which may reduce the efficiency of the steamturbine 36. Accordingly, the steam turbine 36 also includes the faceseal 100 to block or reduce steam 46 flow leakage within the steamturbine 36.

FIG. 3 is a partial cross-sectional view of the steam turbine 36,illustrating an embodiment of the face seal 100, which is configured toblock or reduce steam 46 flow leakage from a first region 102 (e.g., anupstream region) to a second region 104 (e.g., a downstream region) inthe endpacking area. Specifically, the face seal 100 includes a primaryring 106 (a stationary ring) and a mating ring 108 (a rotor ring). Theprimary ring 106 is attached to the inner shell 62 of the steam turbine36 and is moveable in the axial direction 50 only. For example, theprimary ring 106 may be attached to a stationary housing 110 through asecondary seal 118 and anti-rotation feature 128. The mating ring 108(rotor ring) may be an integral part of the shaft 40 (or rotor), orcould be a service-friendly separated component coupled to the shaft 40.Furthermore, the mating ring 108 is secured to the shaft 40 of the steamturbine 36 through mechanical assembling. More specifically, the matingring 108 is secured to the shaft 40 by a first retaining flange 112 anda second retaining flange 114. The first and second retaining flanges112 and 114 cooperatively axially restrain the mating ring 108 to theshaft 40. For example, brazing, welding, mechanical fasteners (e.g.,bolt 116), friction fits, threading, or other retaining mechanisms maybe used to secure the mating ring 108 to the first and second retainingflanges 112 and 114 and secure the first and second retaining flanges112 and 114 to the shaft 40. Bolt 116 tightens flange 114 against theshaft 40 and the flange 112, while preventing compression of and henceany tilting of rotating ring 108. As the shaft 40 is driving intorotation by the steam 46 flowing through the turbine blades 48, themating ring 108 will also be driven into rotation.

Furthermore, the secondary seal 118 (e.g., an annular seal) is disposedbetween the primary ring 106 and the stationary housing 110. With thesecondary seal 118 in place, leakage between the stationary housing 110and primary ring 106 is limited, meanwhile allowing the primary sealring 106 to move axially away or toward the rotating mating ring 108(rotor ring) to accommodate any rotor 40 translation in axial direction50 due to different thermal expansion of rotor 40 relative to stationaryhousing 110, or due to thrust reversal. The secondary seal 118 diameter,or conventionally called pressure-balance diameter, is selected tocontrol primary ring 106 closing force. Similarly, a seal 120 isdisposed between the mating ring 108 and the first retaining flange 112.The seals 118 and 120 are stationary seals. They may block leakage ofsteam 46 or other working fluid between the face seal 100 and thestationary housing 110 and shaft 40. As will be appreciated, in otherembodiments, the face seal 100 may include other numbers or types ofseals to block steam 46 or other working fluid flow between variouscomponents of the face seal 100 and the steam turbine 36.

As shown, the primary ring 106 and the mating ring 108 form a sealinginterface 122. As mentioned above, the sealing interface 122 isconfigured to reduce or block leakage of steam 46 or other working fluidfrom the first region (high pressure region) 102 (e.g., an upstreamregion) to the second region 104 (low pressure region) (e.g., adownstream region) of the steam turbine 36. There is a backing portion126, in which a spring 129 is disposed within a recess 130 and iscoupled to the primary ring 106 and exerts an axial force on the primaryring 106. In this manner, the primary ring 106 may be biased toward themating ring 108 of the face seal 100 to create the seal interface 122.Specifically, as the spring 129 exerts a biasing force on the primaryring 106, a face 132 of the primary ring 106 may be urged toward a face134 of the mating ring 108. Additionally, while the embodiment shown inFIG. 3 illustrates one spring 129 disposed within one recess 130 of thebacking portion 126, other embodiments may include multiple springs 129disposed within respective recesses 130 about a circumference of thebacking portion 126. Similarly, in other embodiments, each recess 130may include multiple springs 129 configured to bias the primary ring 106toward the mating ring 108.

As the mating ring 108 spins with respect to the primary ring 106, thehydrodynamic features (e.g., grooves or pads described in FIGS. 10-13)create a circumferential gradient in the film thickness (gap betweenprimary ring 106 and mating ring 018) that generates hydrodynamicpressure at the interface (at faces 132, 134) and hence a separationforce that keeps the face 132 from contacting face 134 during motion.This happens when the hydrodynamic opening force is larger than the netclosing force created by external pressure acting on primary ring 106and by the spring 129. By selecting the surface features (grooves, padsetc.) of the primary ring 106 and/or mating ring 108, dimensions of theprimary and mating ring 106 and 108, and the spring 129 force, a desiredequilibrium “riding” gap between the primary ring 106 and mating ring108 can be obtained. The leakage volume of steam/gas is determined bythe size of this equilibrium riding gap. If some additional force (e.g.,a transient force due to thermal or pressure transients in operation)causes the mating ring 108 to move towards the primary ring 106, the gapdecreases below the equilibrium value. This reduced gap causes anincrease in the hydrodynamic force at the interface between the primaryring 106 and the mating ring 108. This increased hydrodynamic forceresists the additional force (e.g., a transient force due to thermal orpressure transients in operation) and avoids contact between the primaryring 106 and the mating ring 108 that otherwise would have occurred dueto the additional force. At this point, the dynamic equilibrium isregained at a slightly smaller gap between the primary ring 106 and themating ring 108. On the other hand if the transient perturbations reducethe net closing force, then the hydrodynamic force drops below itsoriginal design value and the dynamic equilibrium is regained at aslightly larger gap between the primary ring 106 and the mating ring 108compared to the original design value. Such a dynamic non-contactoperation while maintaining an almost constant small gap allows the faceseal 100 to operate without mechanical degradation while maintainingvery small leakage. As will be appreciated, the surface features of theprimary ring 106 and mating ring 108 responsible for creatinghydrodynamic pressure distribution and hydrodynamic film stiffness (aswell as dimensions and shape of the primary and mating ring 106 and 108and the spring 129 responsible for creating closing force) can beselected so as to achieve a desired equilibrium riding gap size, andhence desired leakage characteristics and non-contact operation.

As discussed in detail below, in certain embodiments of the face seal100, the primary ring 106 may have a split configuration. Moreparticularly, the primary ring 106 may include two or morecircumferentially split or divided segments that cooperatively form theprimary ring 106. Additionally, the backing portion 126 may have a splitconfiguration. Furthermore, a joint interface between two segments ofthe primary ring 106 may include a roller interface. As such, in themanner described below, the roller interfaces may enable relative axialmovement between the two or more segments of the primary ring 106. Inthis way, face seal 100 performance may improve. For example, therelative axial movement between segments of the primary ring 106 mayreduce or control undesired leakage gaps of the face seal 100, improvedynamic equilibrium of the face seal 100, and/or reduce mechanical wearand degradation of the various components of the face seal 100 duringoperation of the steam turbine 36. Furthermore, the split configurationof the primary ring 106 may enable the use of the face seal 100 withlarger turbines (e.g., steam turbines 36) because the splitconfiguration allows the face seal 100 to be assembled at a particularaxial location directly instead of having to slide the face seal 100from one end of the rotor (shaft) 40, which may not be possible in largediameter turbines. This is one of the major advantages offered by theindividually compliant split ring design.

FIG. 4 is a perspective view of the primary ring 106 of the face seal100. In particular, the illustrated embodiment of the primary ring 106has a split configuration. That is, the primary ring 106 iscircumferentially split into multiple segments. Specifically, in theillustrated embodiment, the primary ring 106 includes a first segment150 and a second segment 152, and the first and second segments 150 and152 cooperatively form the primary ring 106. In other words, the firstand second segments 150 and 152 join together to form the primary ring106. In particular, the first and second segments 150 and 152 join atjoint interfaces 154. As described in further detail below, the jointinterfaces 154 are configured to enable relative axial movement of thefirst and second segments 150 and 152 of the primary ring 106 byincluding a rolling member at the joint interfaces 154. Additionally,while the illustrated embodiment includes the first and second segments150 and 152, other embodiments may include other numbers of segments(e.g., 3, 4, 5, 6, or more) that are circumferentially split andcooperatively form the primary ring 106. Furthermore, in certainembodiments, the backing portion 126 may also have a segmentedconfiguration. For example, in the illustrated embodiment, the firstsegment 150 of the primary ring 106 also includes a first segment 158 ofthe backing portion 126. Similarly, the second segment 152 of theprimary ring 106 also includes a second segment 162 of the backingportion 126. However, in other embodiments, the backing portion 126 andthe primary ring 106 may each have different numbers of segments.

As mentioned above, the first and second segments 150 and 152 abut oneanother at the joint interfaces 154 of the primary ring 106. The segmentjoint interface 154 features overlapped, stepped interfaces to reducedirect leaking path across the joint interface 154. As shown, each jointinterface 154 includes a first joint face 164, a second joint face 166,and a roller joint face 168. In particular, the first joint face 164 andthe roller joint face 168 of each joint interface 154 arecircumferentially 54 offset from one another and generally extend in theradial 52 direction. Additionally, the second joint face 166 of eachjoint interface 154 extends between the first joint face 164 and theroller joint face 168 in the circumferential 54 direction. As such, eachjoint interface 154 has a generally L-shaped configuration. In otherwords, the first and second segments 150 and 152 of the primary ring 106are split along generally L-shaped lines. For example, the first jointface 164 extending generally in the radial 52 direction and the secondjoint face 166 extending generally in the circumferential 54 directionjoin together to form an L-shape. Similarly, the second joint face 166extending generally in the circumferential 54 direction and the rollerjoint face 168 extending generally in the radial 52 direction jointogether to form an L-shape. In the manner described below, thisL-shaped configuration of the joint interfaces 154 between the first andsecond segments 150 and 152 of the primary ring 106 provides a sealingrelationship between the first and second segments 150 and 152 whileenabling relative axial movement between the first and second segments150 and 152 when the primary ring 106 is assembled. The L-shapedconfiguration prevents leakage from the outer diameter of the primaryring 106 because any potential leakage along roller joint face 168 isblocked at the second (e.g., vertical) joint face 166. In other words,the L-shaped configuration creates a tortuous flow path to enable areduction in leakage. Furthermore, along the first joint face 164, shims(e.g., thin metal shims) may be placed to further reduce any potentialleakage.

As will be appreciated, during operation of the steam turbine 36, anouter diameter pressure (e.g., a radially inward pressure represented byarrows 170) of the primary ring 106 may be greater than an innerdiameter pressure (e.g., a radially outward pressure represented byarrows 172) of the primary ring 106. Consequently, the primary ring 106of the face seal 100 may experience a radially inward net pressure.Without a bearing element 174 (roller pins) on the interface 168 toabsorb the inward loading, the radially inward net pressure acting onthe primary seal 106 could cause the first and second segments 150 and152 to be flush or abut one another at the first joint interface 164 andthe second joint face 166 of each joint interface 154. Contact betweenthose interfaces would prevent free relative axial movement betweensegments 150 and 152. Therefore, the first and second joint faces 164and 166 are designed to have a minimal gap while the radially inward netpressure load is carried by the roller pins (e.g., the bearing elements174) on the interface 168. In certain embodiments, the first and secondsegments 150 and 152 may be manufactured to have tight tolerances at thefirst and second joint faces 164 and 166 to minimize the gap and improvethe sealing of the joint interfaces 154. Additionally or alternatively,the joint interfaces 154 may include seal strips disposed in the firstjoint faces 164 to improve sealing of the joint interfaces 154. Thesealing between the first and second joint faces 164 and 166 helps blockundesired leakage of steam 46 or other working fluid across segmentjoints of the face seal 100. Furthermore, in the illustrated embodiment,the symmetrical orientation of the joint interfaces 154 (e.g., first andsecond joint faces 164 and 166) about a vertical axis 173 of the primaryring 106 reduces lateral pressure imbalance.

As mentioned above, the joint interfaces 154 of the primary ring 106each include the roller joint face 168. More specifically, each of theroller joint faces 168 includes one or more roller pins 174 disposedbetween the first and second segments 150 and 152. The cylindrical shapeof the roller pins 174 enable the roller joint faces 168 to carry ortransfer the radially inward net pressure acting on the primary ring 106while still enabling the first and second segments 150 and 152 of theprimary ring 106 to axially (e.g., in the direction 50) move relative toone another. In this manner, each of the first and second segments 150and 152 may achieve its own hydrodynamic equilibrium with respect to themating ring 108 during operation of the steam turbine 36. Morespecifically, as the first and second segments 150 and 152 are free tomove axially independently of one another, any relative tilt between thefirst and second segments 150 and 152 would be corrected bycorresponding hydrodynamic pressures on the first and second segments150 and 152 (e.g., larger hydrodynamic pressures on the segment that iscloser to the mating ring 108 compared to the other segment). Theself-correcting hydrodynamic pressure may cause the segments to moveaxially relative to the other segment until a dynamic equilibrium isre-gained. As a result, the first and second segments 150 and 152 mayoperate or “ride” at their respective equilibrium positions with respectto the mating ring 108 while reducing the occurrence of rubbing betweenthe first and second segments 150 and 152 and the mating ring 108. Inthis manner, mechanical degradation of the face seal 100 may be reduced,face seal 100 life span may be improved, and maintenance may be reduced.

FIG. 5 is a partial cross-sectional view of an embodiment of the faceseal 100, illustrating the primary ring 106 having locally complianthydrodynamic pads 200. Specifically, the locally compliant hydrodynamicpads 200 are disposed in and adjacent the primary ring 106 facing themating ring 108 of the face seal 100. That is, the illustrated locallycompliant hydrodynamic pad 200 is disposed within a pocket or recess 202of the primary ring 106. Additionally, the hydrodynamic pads 200 mayeach be biased towards the mating ring 108 by one or more springs 204(e.g., coil spring). As a result, the hydrodynamic pads 200 areconfigured to engage with the mating ring 108. One of the functions ofthe locally compliant hydrodynamic pad 200 is to engage the mating ring108 before the majority of the primary ring face 132 comes close to themating ring face 134. The locally compliant hydrodynamic pad 200 alsohelps align the primary ring 106 properly with the mating ring 108.Furthermore, in certain embodiments, each of the hydrodynamic pads 200may have a micron length-scale profile (e.g., on axial face 206 of thehydrodynamic pad 200) with axial groove depth variations in thecircumferential direction 54 of each hydrodynamic pad 200 and/or in theradial direction 52 of each hydrodynamic pad 200 to generate a specificprofile of hydrodynamic pressure on each hydrodynamic pad 200 to helpthe face seal 100 maintain non-contact operation. Similarly, it shouldbe noted that primary ring sealing face 208 and/or the mating ringsealing face 210 of may also have various profiles or surface featuresto improve hydrodynamic load-bearing performance of the face seal 100,as discussed in detail below.

As mentioned, the spring 204 is disposed within the respective pocket orrecess 202 of the primary ring 106. That is, the recess 202 is formed inthe primary ring 106 that faces the mating ring 108 of the face seal 100when the face seal 100 is assembled. As will be appreciated, the spring204 is designed to allow certain degrees of freedom for the hydrodynamicpad 200. For example, the spring 204 may allow a first translationaldegree of freedom in an out of the plane of the primary ring 106 (e.g.,movement in the axial direction 50), a second rotating degree of freedomrocking or pivoting in the circumferential direction 54, and a thirdrotating degree of freedom rocking or pivoting in the radial direction52. Therefore, the hydrodynamic pad 200 may better conform to the matingring 108 orientations and/or distortions. As a result, the hydrodynamicpad 200 may block contact between the primary ring 106 and the matingring 108, while also blocking the formation of large leakage gapsbetween the primary ring 106 and the mating ring 108 of the face seal100. In other words, the hydrodynamic pad 200 enables the primary ring106 to maintain a “hydrodynamically locked in” position with respect tothe mating ring 108. A local closing force facilitated by individualpocket spring 204 and a local hydrodynamic opening force facilitated byindividual pad 200 help the primary ring 106 perform with precision soas to achieve a dynamic equilibrium with respect to the mating ring 108without contacting the mating ring 108. This can help prevent or reducerubs when the operating forces are trying to form a wedge shaped gapbetween the primary ring 106 and mating ring 108. During such an event,the pads 200 on the primary ring 106 that are closer to the mating ring108 will tend to generate a larger hydrodynamic opening force and willcompress corresponding local springs 204 farther into the backingportion 126 compared to the pads 200 that are away from the mating ring108. This radial difference in opening force will create a nutation ofthe primary ring 106 and will try to make the wedge shaped gap parallel.The ability of the face seal 100 to ride with such a parallel gapreduces the possibility of rubbing. In this manner, rubbing andmechanical degradation between the primary ring 106 and mating ring 108may be reduced while still maintaining the leakage of steam 46 to a verylow designed value. As will be appreciated, a reduction in mechanicaldegradation of components of the face seal 100 may reduce steam turbine36 down time and maintenance costs and may increase the useful life ofthe face seal 100 components, while a reduction of steam 46 leakage mayimprove efficiency of the steam turbine 36.

As mentioned above, the axial face 206 of each hydrodynamic pad 200 mayhave various profiles to improve operation of the face seal 100. Forexample, the face 206 of one or more hydrodynamic pads 200 may have aconverging profile in the direction of rotation (e.g., in thecircumferential direction 54) to enable hydrodynamic force generation asthe mating ring 108 spins past them in one direction (e.g. clockwise).In other embodiment pads 200 can have a wavy profile to enablebi-directional operation of the steam turbine 36. In another embodiment,the face 206 of one or more hydrodynamic pads 200 may have a step in theradial direction 52 that forms a dam section against radially 52 inwardflow of steam 46 to generate an additional dynamic pressure component(due to flow impingement) that will improve hydrodynamic pressuredistribution. Such features may help reduce tolerance demand orrequirements of various face seal 100 components. It should be notedthat the sealing face 208 of the primary ring 106 and the sealing face210 of the mating ring 108 may also have various profiles or surfacefeatures to improve hydrodynamic load-bearing performance of the faceseal 100.

Furthermore, the number of springs 204 biasing each hydrodynamic pad 200and the position of the springs 204 relative to the respectivehydrodynamic pad 200 may vary in different embodiments. For example, inthe illustrated embodiment, the hydrodynamic pad 200 is biased towardthe mating ring 108 by one spring 204 that is generally coupled to acenter of the hydrodynamic pad 200. In other embodiments, eachhydrodynamic pad 200 may have multiple springs 204 biasing thehydrodynamic pad 200 toward the mating ring 108. For example, eachhydrodynamic pad 200 may be biased toward the mating ring 108 by foursprings 204 with one spring 204 coupled to a respective corner of thehydrodynamic pad 200 (see FIG. 8). For further example, in certainembodiments, each hydrodynamic pad 200 may include one spring 204coupled to the hydrodynamic pad 200 offset from the center (e.g.,radially 52 inward or radially 52 outward) of the hydrodynamic pad 200.Leaf springs could be used instead of the coil springs shown.

FIGS. 6 and 7 are perspective views of an embodiment of the primary ring106 of the face seal 100, illustrating locally compliant hydrodynamicpads 200 of the primary ring 106. As mentioned above, each of thelocally compliant hydrodynamic pads 200 may be supported by one or moresprings 204. As a result, each of the hydrodynamic pads 200 can moveindividually (e.g., irrespective of other hydrodynamic pads 200) in andout of the plane of the primary ring 106. In this manner, each of thehydrodynamic pads 200 may conform to the dynamically changingorientation of the mating ring 108 arising from thermal,pressure-driven, and/or transient forces.

In the illustrated embodiment, the primary ring 106 includes six locallycompliant hydrodynamic pads 200 spaced substantially equidistantly aboutthe primary ring 106 in the circumferential direction 54. However, inother embodiments, the primary ring 106 may include other numbers ofhydrodynamic pads 200 and/or hydrodynamic pads 200 arranged in otherconfigurations, as discussed below. For example, in the illustratedembodiment, the hydrodynamic pads 200 have substantially similarpositions along the primary ring 106 in the radial direction 52.However, in other embodiments, the hydrodynamic pads 200 may be radially52 staggered. For example, one hydrodynamic pad 200 may have a firstradial 52 position, and adjacent hydrodynamic pads 200 may have a secondradial 52 position, thereby creating a staggered arrangementcircumferentially 54 around the primary ring 106.

Furthermore, the illustrated embodiment of the primary ring 106 includesthe first and second segments 150 and 152, as similarly described abovewith respect to FIG. 4. Additionally, the joint interfaces 154 of theprimary ring 106 include the roller pins 174 to enable relative axial 50movement of the first and second segments. However, it should be notedthat other embodiments of the primary ring 106 may include the locallycompliant hydrodynamic pads 200 but not a segmented configuration.Similarly, in other embodiments, the primary ring 106 may include asegmented configuration but not the locally compliant hydrodynamic pads200 described above.

FIGS. 8 and 9 are perspective views of other embodiments of the primaryring 106 of the face seal 100, illustrating locally complianthydrodynamic pads 200 of the primary ring 106. Specifically, FIG. 8illustrates the primary ring 106 having locally compliant hydrodynamicpads 200, where each locally compliant hydrodynamic pad 200 is biasedtoward the mating ring 108 by four springs 204 within the respectiverecess 202cut through the face of the primary ring 106. As shown, eachrecess 202 includes one spring 204 in each of the four corners of therecess 202. Such an arrangement provides the ability to tune the spring204 stiffness at the four corners of the pad 200 individually so as toprovide desired moment characteristics to correct for any tilt bias inthe primary ring 106. For example, by increasing the stiffness of thesprings 204 at the top corners, one can make area near the outerdiameter of the pad 200 less compliant with respect to the innerdiameter, thus causing fluid film thickness locally higher at the innerdiameter of the pad 200 than at the outer diameter so as to compensatefor any tilt-producing operational phenomenon that causes inner diameterfilm thickness to be lower than the outer diameter film thickness. Inthe illustrated embodiment, the springs 204 are coil springs, however,in other embodiments, the springs 204 may be other types of springs,such as leaf spring or beams. FIG. 9 illustrates an embodiment of theprimary ring 106 having locally compliant hydrodynamic seals 200, whereeach of the locally complaint hydrodynamic seals 200 are biased by arespective bellow spring 300 disposed within the respective recess 202of the primary ring 106. By selecting the thickness of the bellows,spacing between bellow turns and number of turns, one can achieve thedesired force and structural moment characteristics of compliantmechanism of the pad to resist any aerodynamic moments (e.g. due towindage) that are trying to de-stabilize the hydrodynamic performance ofthe seal. While each locally complaint hydrodynamic seal 200 is biasedby one bellow spring 300 in the illustrate embodiment, other embodimentsmay include other numbers of bellow springs 300.

FIGS. 10 and 11 are perspective views of other embodiments of theprimary ring 106 of the face seal 100, illustrating another arrangementof the locally compliant hydrodynamic pads 200 of the primary ring 106.Specifically, in FIGS. 10 and 11, the primary ring 106 includes a first,radially inward set 310 of locally compliant hydrodynamic pads 200, anda second, radially outward set 312 of locally compliant hydrodynamicpads 200. Additionally, the first, radially inward set 310 and thesecond, radially outward set 312 of locally compliant hydrodynamic padsare staggered circumferentially 54 about the primary ring 106 withrespect to one another. However, in other embodiments, the first,radially inward set 310 and the second, radially outward set 312 may notbe circumferentially staggered relative to one another. Additionally, aswill be appreciated, the first, radially inward set 310 and the second,radially outward set 312 may have the same or different numbers oflocally compliant hydrodynamic pads 200. Furthermore, in FIG. 11, eachof the second, radially outward set 312 of locally complianthydrodynamic pads 200 includes a surface treatment 314. Specifically,each of the second, radially outward set 312 of locally complianthydrodynamic pads 200 includes a micron length-scale profile or grooves314 on the respective face 206 of each hydrodynamic pad 200. As will beappreciated, the micro-scale profile or grooves 314 on the respectiveface 206 of each hydrodynamic pad 200 may generate additional pressuretowards an inner diameter 316 of the primary ring 106, thus providingadditional hydrodynamic separation force to keep the primary ring 106from contacting the mating ring 108.

FIGS. 12 and 13 are perspective views of other embodiments of theprimary ring 106 of the face seal 100, illustrating various surfacetreatments or features formed on the sealing face 208 of the primaryring 106. For example, in FIG. 12, the sealing face 208 of the primaryring 106 includes grooves 320 (e.g., spiral grooves), which extend froman outer diameter 322 toward an inner diameter 324 of the sealing face208. As will be appreciated, the grooves 320 may be recesses formed inthe sealing face 208 that extend toward, but not all the way to, theinner diameter 324 of the sealing face 208. Rather, each groove 320 hasa dam portion 326. As such, steam 46 or other gas may enter the grooves320 from the outer diameter side during operation of the steam turbine36 and flow through the grooves, accelerating along the curvature of thegrooves, towards the dam portion 326 of each groove 320 and finallyimpinges against the dam portion 326, thus creating a dynamic pressurerise so as to provide the hydrodynamic separation force. In this manner,the grooves 320 may enable the generation of additional pressure towardthe inner diameter 324 of the primary ring 106. In FIG. 13, the sealingface 208 of the primary ring 106 includes Y-shaped grooves 330. Asshown, each Y-shaped groove 330 extends from the middle of sealing face208 toward both outer diameter 322 and the inner diameter 324 startingfrom a stem portion 332 to form a Y-shaped groove 330 which isterminated before reaching the inner and outer diameters. As steam 46 orother gas is fed into the Y-shaped grooves 330 through hole 334. TheY-shaped grooves 330 pumps fluid toward both outer diameter 322 and theinner diameter 324 simultaneously to generate hydrodynamic pressure inthe regions near the outer or inner diameters 322 or 324 of the primaryring 106. With such a Y shaped configuration of the grooves, the outerbranch and inner branch of the Y shape provide the self-correctinghydrodynamic forces needed to follow any coning of the mating ringsealing face 210.

As will be appreciated, each of the features (e.g., surface treatmentsand/or profiles) of the embodiments discussed above may be includedindividually or in any combination with one another as a part of one ormore of the different components of the face seal 100. For example, thehydrodynamic features shown on the primary sealing face 208 in FIGS. 12and 13 can be applied to the mating ring sealing face 210 while theprimary sealing face 208 is a blank flat surface. Additionally, one ofordinary skill in the art will appreciate that the various arrangements,surface treatments, and other features discussed above may have otherconfigurations, which are considered within the scope of the presentdisclosure.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

1. A system, comprising: a steam turbine; and a face seal of the steamturbine, comprising: a rotor ring coupled to a rotor of the steamturbine; and a stator ring coupled to a stationary housing of the steamturbine, wherein the stator ring is circumferentially split into aplurality of circumferential segments with one or more bearing elementsdisposed between each of the plurality of circumferential segments,wherein the one or more bearing elements are configured to enablerelative axial movement of the plurality of segments relative to oneanother, hydrodynamic surface features on a sealing surface of at leastone of the rotor ring and the stator ring facing the other of the rotorring and the stator ring, wherein the hydrodynamic surface featurescomprise Y-shaped grooves each comprising a stem portion extending froma middle region of the rotor ring or the stator ring and splitting intoinner and outer branches extending towards inner and outer diameters ofthe rotor ring or the stator ring respectively.
 2. The system of claim 1wherein the inner and outer branches of the Y-shaped grooves terminateprior to the respective inner and outer diameters.
 3. The system ofclaim 2 further comprising a plurality of holes for feeding a gas intothe stem portions of respective ones of the Y-shaped grooves.
 4. Thesystem of claim 1 wherein the rotor ring comprises the Y-shaped grooves.5. The system of claim 1 wherein the stator ring comprises the Y-shapedgrooves.
 6. The system of claim 5 wherein the Y-shaped grooves aresituated on the circumferential segments.
 7. The system of claim 5further comprising a plurality of pads configured to extend from thecircumferential segments, wherein the Y-shaped grooves are situated onthe plurality of pads.
 8. A turbine, comprising: a rotor; a stationaryhousing disposed about the rotor; and a face seal disposed about therotor, comprising: a rotor ring coupled to or integral with the rotor;and a stator ring coupled to the stationary housing, wherein the statorring comprises: a first segment; a second segment; and at least twobearing elements, wherein the first and second segments arecircumferentially split, and the at least two bearing elements aredisposed between the first and second segments, and wherein the firstsegment, the second segment, and the at least two bearing elementscooperatively form the stator ring, hydrodynamic surface features on asealing surface of at least one of the rotor ring and the stator ringfacing the other of the rotor ring and the stator ring, wherein thehydrodynamic surface features comprise Y-shaped grooves each comprisinga stem portion extending from a middle region of the rotor ring or thestator ring and splitting into inner and outer branches extendingtowards inner and outer diameters of the rotor ring or the stator ringrespectively.
 9. The turbine of claim 8 wherein the inner and outerbranches of the Y-shaped grooves terminate prior to the respective innerand outer diameters.
 10. The turbine of claim 9 further comprising aplurality of holes for feeding a gas into the stem portions ofrespective ones of the Y-shaped grooves.
 11. The turbine of claim 8wherein the rotor ring comprises the Y-shaped grooves.
 12. The turbineof claim 8 wherein the stator ring comprises the Y-shaped grooves. 13.The system of claim 12 wherein the Y-shaped grooves are situated on thefirst and second segments.
 14. The system of claim 12 further comprisinga plurality of pads configured to extend from the first and secondsegments, wherein the Y-shaped grooves are situated on the plurality ofpads.
 15. A system, comprising a stator ring configured to be disposedabout a rotor of a turbine, wherein the stator ring comprises a firstring segment and a second ring segment which are circumferentially splitand configured to cooperatively form the stator ring, at least onebearing element disposed between the first and second ring segments andconfigured to enable relative axial motion between the first and secondring segments at interfaces between the first and second ring segments,hydrodynamic surface features on surfaces of the first and second ringsegments configured for facing the rotor, wherein the hydrodynamicsurface features comprise Y-shaped grooves each comprising a stemportion extending from a middle region of stator ring and splitting intoinner and outer branches extending towards inner and outer diameters ofthe stator ring and terminating prior to the inner and outer diameters.16. The system of claim 15 further comprising a plurality of holes forfeeding a gas into the stem portions of respective ones of the Y-shapedgrooves.